Polymers are used extensively in a wide range of medical applications such as biomaterials incorporated into drug delivery systems, diagnostic applications or prosthetic devices. The successful application of polymers for such purposes remains problematic, however. These problems reside in part due to the manner in which such polymers are cross-linked to form biomaterials.
For example, the use of polymers as gel compositions to encapsulate a drug requires that the structure of the gel composition produced from the polymers be carefully formulated to ensure the release of the drug over a desired interval of time. It may be difficult, however, using conventional gels to achieve the desired rate of release. In addition, the steps used to prepare the gel composition may be incompatible with the drug the gel composition is designed to contain. For example, the preparation of a polyacrylamide based cross-linked hydrogel typically involves the formation of a free radical on the growing polymer chain and cross-linking chains. Such free radicals or other chemical intermediaries may alter or inactivate the drug. Therefore, additional processing steps must be taken to prepare a capsule, and then add the drug to the capsule, often with the addition of waxes, fats or other filler material to help the capsule maintain its shape.
The use of polymers to make biomaterials comprising gel compositions used as prosthetic devices may be limited by the mechanical properties of the gel, or the synthetic procedures used to form such gels. It may be difficult, for example, to prepare a gel composition whose stress-strain relationship adequately mimics the biological material the gel is intended to replace, including soft tissues such as the nucleus pulposus present in intervertebral discs. Similar to that discussed above, the steps used to prepare the gel composition, resulting in the generation of free radicals for example, may make it undesirable to form the biomaterial in situ. Moreover, the monomer and cross-linking molecule may have toxicity or carcinogenic properties, such as acrylamide and N, N′ methylene bis acrylamide. In certain applications, it may be desirable to alter the shape or mechanical properties of the biomaterial. For many conventional gel compositions this may necessitate the undesirable heating of the material.
Accordingly, what is needed in the art is a new gel composition that does not experience the problems associated with previous gels.